1. Field of the Invention
The present invention is directed to a piezoelectrically operated head for ink-jet printer units having printing jets in which a printing liquid contained in a compression chamber which is surrounded by a cylindrical piezoelectric drive element is ejected in a droplet fashion by a piezoelectric contraction of the drive element.
2. Prior Art
An electrically operated printing unit in which a printing jet is made to execute mechanical vibrations by means of a piezoelectric drive element to eject printing liquid in droplet form is disclosed in U.S. Pat. No. 3,298,030. After each droplet of printing liquid or ink is ejected from the jet, the droplet is deflected to one of several different positions by an electrical field to form characters on a recording medium and the amount of deflection of each droplet is controlled by a character generator.
In order for this type of printing unit to achieve an adequate high printing speed along with sufficient ink saturation on the parts of the characters being recorded, the frequency of release of the individual droplets of ink must be extremely high. Due to this extremely high release frequency, the overall unit is relatively highly susceptible to breakdowns. Also, since the printing device must synchronize each individual droplet with the associated deflection voltage, the synchronizing devices, which are required, are also susceptible to breakdowns.
In order to overcome the above-mentioned drawbacks, several printing units have been combined to form a single printer head as disclosed in German Offenlegungsschrift No. 2,262,106. In this device, the single head is moved in a manner of a mosaic printer head in a line fashion along a data carrier with each grid point being assigned a piezoelectrically operated printing jet. In this particular device, a piezoelectric crystal transducer acts upon a diaphragm to develop a requisite pressure in a compression chamber to cause the release of an ink droplet. However, with this device, special design difficulties are created.
These difficulties result from the physical dimensions of the individual piezoelectrically operated jets and their drive arrangements which must be grouped together in accordance with the size of the printing grid. The frequent changes, which occur in the printing operation between the phases of acceleration and deceleration, for example a start-stop operation, also requires that the overall printer head must have the lowest possible mass.